In the aluminum chloride market there is a demand for products ranging from solutions that contain free hydrochloric acid to products, both liquid and dry, of increasing levels of basicity. Aluminum chloride has the general chemical formula of Aln(OH)mCl3n-m. Basicity is defined as the ratio of
      m          3      ⁢      n        .where m is less than or equal to 5.2.
It is undesirable to use elemental aluminum as the source of aluminum to produce these products due to the controlled availability and volatility of pricing of the metal on the commodity market. Sources of aluminum such as aluminum ore (bauxite), refined aluminum ore (aluminum trihydrate (ATH)) or various pre-solubilized forms are more desirable because of their availability and relatively stable pricing.
Production of high basicity products starting with aluminum from non-metallic sources requires rapidly increasing amounts of energy as basicity increases. In addition to the energy, the stability of the final product begins to decrease once the basicity ratio is greater than 0.3. From this point (0.3 basicity ratio) up to a basicity ratio of 0.83 technology similar to that disclosed in U.S. Pat. No. 5,985,234 can be used, typically with aluminum metal as a starting material.
An alternate approach for increasing the basicity ratio is to remove chloride from the molecule rather than adding aluminum. Under this approach, a simple solution of aluminum chloride is produced using a non-elemental source of aluminum. It is known that solutions of aluminum chloride when concentrated beyond saturation form crystals of aluminum chloride hexahydrate and that these crystals, when exposed to heat, decompose, releasing hydrogen chloride and water. This approach has been applied to produce high purity aluminum oxide and, to a lesser extent, to produce basic aluminum chloride, but only in batching operations. A process that reduces the requirement of batching operations would result in increased efficiency of production, lower cost, and improved safety.
Several publications describe systems that utilize mills and rotational motion for dehydration and drying materials. See e.g., U.S. Pat. Nos. 6,145,765; 5,167,372; 4,390,131; 3,462,086; 2,470,315; and U.S. publication number 2004/0040178. These systems do not address issues associated with the stringent requirements, such as handling of evolved hydrochloric acid that must be addressed in the production of aluminum chloride products of specific basicity. In another approach, flash dryer systems involve spraying slurry onto a dryer and applying high temperature to evaporate gas and liquid components. See e.g., U.S. Pat. No. 5,573,582.
Evaporation, crystallization, and recovery of formed crystals are well known in the art. See for example, McCabe and Smith 1976, Unit Operations of Chemical Engineering, in particular, the following sections: Evaporation, pages 425-463 to 11-118, Crystallization, pages 852 to 894, and Filtration, pages 922 to 953; and Perry's Chemical Engineering Handbook (7th Ed. Perry and Green, 1999), sections: Evaporation, pages 11-107 to 11-118, Crystallization, pages 18-35 to 18-55, and Filtration, pages 18-74 to 18-125.